The maximum energy of a tritium beta particle is only 18.5 Kev, so that its maximum range in air at normal atmospheric pressure is only 1.5 mm. Furthermore, when monitoring such radiation it is necessary to exclude all light.
It is an object of the invention in its preferred form to provide a portable apparatus for measurement of nuclear radiation which is easy for a worker in the radioactivity art to use for measuring tritium contamination of a surface area, article or quantity of matter. However, the invention may have application having nothing to do with this object.